Circulating suPAR in two cohorts of primary FSGS

A case report of adrenocorticotropic hormone to treat recurrent focal segmental glomerular sclerosis post-transplantation and biomarker monitoring

Background: Recurrent focal segmental glomerular sclerosis (rFSGS) in renal transplant recipients (RTR) is difficult to predict and treat. Early rFSGS is likely from circulating factors and preformed antibodies.

Methods: We present the case of a 23-year-old white man who presented with rFSGS and acute renal failure, requiring dialysis 9-months after a 1-haplotype matched living-related transplant. We retrospectively analyzed serum samples from various clinical stages for rFSGS biomarkers: serum glomerular albumin permeability (P_alb), soluble urokinase-type plasminogen activator receptor (suPAR) serum level with suPAR-β3 integrin signaling on human podocytes, and angiotensin II type I receptor-antibody (AT1R-Ab) titer.

Results: All biomarkers were abnormal at 1-year pre-transplant prior to initiation of dialysis and at the time of transplant. After initiation of hemodialysis, β3 integrin activity on human podocytes, in response to patient serum, as well as AT1R-Ab were further elevated. At the time of biopsy-proven recurrence, all biomarkers were abnormally high. One week after therapy with aborted plasmapheresis (secondary to intolerance), and high dose steroids, the P_alb and suPAR-β3 integrin activity remained significantly positive. After 12-weeks of treatment with high-dose steroids, rituximab, and galactose, the patient remained hemodialysis-dependent. Three-months after his initial presentation, we commenced adrenocorticotropic hormone (ACTH, Acthar^® Gel), 80 units subcutaneously twice weekly. Four-weeks later, he was able to discontinue dialysis. After 8-months of maintenance ACTH therapy, his serum creatinine stabilized at 1.79 mg/dL with <1 g of proteinuria.

Conclusion: ACTH therapy was associated with improvement in renal function within 4 weeks. The use of rFSGS biomarkers may aid in predicting development of rFSGS.

Recent advances in the understanding of immune-mediated nephrotic syndrome: diagnostic and prognostic implications

Glomerular diseases with severe defects in glomerular permeability give rise to heavy proteinuria and can present as nephrotic syndrome. There are many different causes of the nephrotic syndrome and a renal biopsy is nearly always needed to elucidate the underlying disease. During the last decade, substantial advances have occurred in the understanding of the pathophysiological mechanisms involved in immune-mediated glomerular diseases. Here, we review the diagnostic and prognostic implications of recent progress on the understanding of membranous nephropathy, minimal change disease, focal segmental glomerulosclerosis, amyloidosis, IgA nephropathy and membranoproliferative glomerulonephritis.

Biomarkers of kidney injury and klotho in patients with atherosclerotic renovascular disease

BACKGROUND AND OBJECTIVES

Occlusive renovascular disease and hypertension may progress to CKD. Circulating levels of several biomarkers, including fibroblast growth factor (FGF)-23, Klotho, and soluble urokinase plasminogen activator receptor (suPAR), are altered in patients with CKD, but their role in essential hypertension (EH) and renovascular hypertension (RVH) remains unclear.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Levels of FGF-23, Klotho, suPAR, plasminogen activator inhibitor (PAI)-1, tissue factor, and tissue factor pathway inhibitor (TFI) were measured in the inferior vena cava and renal vein of hypertensive patients with atherosclerotic renal artery stenosis (n=12) or age-matched participants with EH (n=12) and relatively preserved renal function. Single-kidney blood flow was measured to calculate renal release of markers. For control, peripheral vein levels were measured in healthy volunteers (HVs; n=12).

RESULTS

FGF-23 levels did not differ among the groups, whereas Klotho levels were lower in participants with RVH and EH than in HVs, and suPAR levels were elevated in patients with RVH compared with HVs and patients with EH (6.1±1.5 versus 4.4±1.9 and 3.2±1.2 ng/ml, P<0.05). PAI-1 levels were higher in patients with RVH than in patients with EH, but tissue factor and TFI levels were not statistically significantly different. After adjustment for GFR, Klotho levels remained decreased in both RVH and EH, and suPAR and PAI-1 levels remained elevated in RVH. eGFR correlated inversely with systemic and renal vein suPAR levels, and directly with systemic Klotho levels.

CONCLUSIONS

Klotho levels are low in hypertensive patients, whereas suPAR and PAI-1 levels are specifically elevated in RVH, correlating with GFR. Klotho, PAI-1, and suPAR may be markers of kidney injury in hypertensive patients.

Case series: CTLA4-IgG1 therapy in minimal change disease and focal segmental glomerulosclerosis

BACKGROUND

Minimal Change Disease (MCD) in relapse is associated with increased podocyte CD80 expression and elevated urinary CD80 excretion, whereas focal segmental glomerulosclerosis (FSGS) has mild or absent CD80 podocyte expression and normal urinary CD80 excretion.

METHODS

One patient with MCD, one patient with primary FSGS and three patients with recurrent FSGS after transplantation received CD80 blocking antibodies (abatacept or belatacept). Urinary CD80 and CTLA-4 levels were measured by ELISA. Glomeruli were stained for CD80.

RESULTS

After abatacept therapy, urinary CD80 became undetectable with a concomitant transient resolution of proteinuria in the MCD patient. In contrast, proteinuria remained unchanged after abatacept or belatacept therapy in the one patient with primary FSGS and in two of the three patients with recurrent FSGS despite the presence of mild CD80 glomerular expression but normal urinary CD80 excretion. The third patient with recurrent FSGS after transplantation had elevated urinary CD80 excretion immediately after surgery which fell spontaneously before the initiation of abatacept therapy; after abatacept therapy, his proteinuria remained unchanged for 5 days despite normal urinary CD80 excretion.

CONCLUSION

These observations are consistent with a role of podocyte CD80 in the development of proteinuria in MCD. In contrast, CD80 may not play a role in recurrent FSGS since the urinary CD80 of our three patients with recurrent FSGS was only increased transiently after surgery and normalization of urinary CD80 did not result in resolution of proteinuria.

Novel therapies for FSGS: preclinical and clinical studies

Focal segmental glomerulosclerosis (FSGS) is a rare but important cause of end-stage kidney disease in children and adults. Current therapy, consisting of corticosteroids and calcineurin inhibitors, fails to achieve a sustained remission in most patients. Therefore, there is a pressing need to develop new treatments for this glomerulopathy. Traditional approaches have focused on agents that modulate the immune system. In this review, we summarize preclinical and clinical data with newer agents that may ameliorate FSGS. We focus on drugs that inhibit immune injury or inflammation, such as abatacept, rituximab, adalimumab, and stem cells. The potential of agents that block the glomerular action of circulating permeability factors such as soluble urokinase receptor is reviewed. Finally, because fibrosis represents the final common pathway of glomerular damage in FSGS, the experience with a wide range of antifibrotic agents is presented. Despite extensive research on the podocyte dysfunction in the pathogenesis of FSGS, there are few agents that directly target podocyte structure or viability. We conclude that FSGS is a heterogeneous disorder and that intensified translational research is vital to improve our understanding of distinct subtypes that have a defined prognosis and predictable response to targeted therapeutic interventions.

Serum suPAR levels help differentiate steroid resistance from steroid-sensitive nephrotic syndrome in children

BACKGROUND

Soluble urokinase plasminogen activator receptor (suPAR) has been regarded as a permeability factor in proteinuria, though its role in primary nephrotic syndrome remains to be elucidated further.

METHODS

Plasma samples and clinical information from 176 children with primary nephrotic syndrome were collected and concentrations of suPAR were measured. We evaluated the correlation between suPAR concentrations and clinical features, and the value of the plasma suPAR level in predicting steroid-resistant nephrotic syndrome (SRNS).

RESULTS

There is a significant difference in plasma suPAR concentration between SRNS and steroid-sensitive nephrotic syndrome (SSNS) groups (3,744.1 ± 2,226.0 vs. 2,153.5 ± 1,167.0, p < 0.05). The area under the curve (AUC) was 0.80, with p < 0.001 for the receiver operating characteristic (ROC) curve analysis using suPAR to predict SRNS. The suspicious range for predicting SRNS was estimated to be 1,907.0 pg/ml to 3,043.5 pg/ml (χ(2) = 14.775, p = 0.001).

CONCLUSIONS

From ROC curve analysis, we demonstrated the significance of the suPAR level in predicting SRNS with a high specificity but low sensitivity. However, the clinical value of suPAR to predict steroid resistance and guide therapy remains to be investigated further.

Rituximab in Children with Steroid-Dependent Nephrotic Syndrome: A Multicenter, Open-Label, Noninferiority, Randomized Controlled Trial

Steroid-dependent nephrotic syndrome (SDNS) carries a high risk of toxicity from steroids or steroid-sparing agents. This open-label, noninferiority, randomized controlled trial at four sites in Italy tested whether rituximab is noninferior to steroids in maintaining remission in juvenile SDNS. We enrolled children age 1-16 years who had developed SDNS in the previous 6-12 months and were maintained in remission with high prednisone doses (≥0.7 mg/kg per day). We randomly assigned participants to continue prednisone alone for 1 month (control) or to add a single intravenous infusion of rituximab (375 mg/m(2); intervention). Prednisone was tapered in both groups after 1 month. For noninferiority, rituximab had to permit steroid withdrawal and maintain 3-month proteinuria (mg/m(2) per day) within a prespecified noninferiority margin of three times the levels among controls (primary outcome). We followed participants for ≥1 year to compare risk of relapse (secondary outcome). Fifteen children per group (21 boys; mean age, 7 years [range, 2.6-13.5 years]) were enrolled and followed for ≤60 months (median, 22 months). Three-month proteinuria was 42% lower in the rituximab group (geometric mean ratio, 0.58; 95% confidence interval, 0.18 to 1.95 [i.e., within the noninferiority margin of three times the levels in controls]). All but one child in the control group relapsed within 6 months; median time to relapse in the rituximab group was 18 months (95% confidence interval, 9 to 32 months). In the rituximab group, nausea and skin rash during infusion were common; transient acute arthritis occurred in one child. In conclusion, rituximab was noninferior to steroids for the treatment of juvenile SDNS.

Clinical Features and Histology of Apolipoprotein L1-Associated Nephropathy in the FSGS Clinical Trial

Genetic variants in apolipoprotein L1 (APOL1) confer risk for kidney disease. We sought to better define the phenotype of APOL1-associated nephropathy. The FSGS Clinical Trial involved 138 children and young adults who were randomized to cyclosporin or mycophenolate mofetil plus pulse oral dexamethasone with a primary outcome of proteinuria remission. DNA was available from 94 subjects who were genotyped for APOL1 renal risk variants, with two risk alleles comprising the risk genotype. Two APOL1 risk alleles were present in 27 subjects, of whom four subjects did not self-identify as African American, and 23 of 32 (72%) self-identified African Americans. Individuals with the APOL1 risk genotype tended to present at an older age and had significantly lower baseline eGFR, more segmental glomerulosclerosis and total glomerulosclerosis, and more tubular atrophy/interstitial fibrosis. There were differences in renal histology, particularly more collapsing variants in those with the risk genotype (P=0.02), although this association was confounded by age. APOL1 risk genotype did not affect response to either treatment regimen. Individuals with the risk genotype were more likely to progress to ESRD (P<0.01). In conclusion, APOL1 risk genotypes are common in African-American subjects with primary FSGS and may also be present in individuals who do not self-identify as African American. APOL1 risk status is associated with lower kidney function, more glomerulosclerosis and interstitial fibrosis, and greater propensity to progress to ESRD. The APOL1 risk genotype did not influence proteinuria responses to cyclosporin or mycophenolate mofetil/dexamethasone.

Clinical significance of serum and urinary soluble urokinase receptor (suPAR) in primary nephrotic syndrome and MPO-ANCA-associated glomerulonephritis in Japanese

BACKGROUND

The soluble urokinase receptor (suPAR) has been implicated as a cause of primary focal segmental glomerulosclerosis (FSGS). However, the clinical significance of suPAR in glomerular diseases currently remains unclear.

METHODS

In this retrospective single-center cohort study, we investigated serum (s-) and urinary (u-) suPAR in patients with primary nephrotic syndrome (NS) (serum/urine: 37/32 cases) and MPO-ANCA-associated glomerulonephritis (ANCA-GN) (serum/urine: 13/11 cases).

RESULTS

In pretreatment s- and u-suPAR, no significant differences were observed between the primary NS and ANCA-GN groups or among the pathological types of primary NS. An inverse correlation was noted between pretreatment s-suPAR and eGFR in the primary NS and ANCA-GN groups. A positive correlation was noted between pretreatment u-suPAR and proteinuria in the primary NS group. Furthermore, time-course changes in s- and u-suPAR over 2 months after therapy were associated with the therapeutic responsiveness of primary NS, particularly the differentiation of MCNS from FSGS (s-suPAR: AUC-ROC = 0.905, p = 0.007; u-suPAR: AUC-ROC = 0.816, p = 0.048). In the ANCA-GN group, a positive correlation was found between pretreatment s-suPAR and clinical severity or crescent formation, whereas u-suPAR was not correlated with these parameters.

CONCLUSION

S- and u-suPAR after therapy may serve as clinical markers to judge the treatment response of untreated NS and differentiate MCNS from FSGS, but not in pretreatment patients. S-, but not u-suPAR may predict the severity of and crescent formation in ANCA-GN.

Serum suPAR levels are modulated by immunosuppressive therapy of minimal change nephrotic syndrome

BACKGROUND

Soluble urokinase-type plasminogen activator receptor (suPAR) could be a causative factor in idiopathic focal segmental glomerulosclerosis (FSGS). It is currently unknown to what extent suPAR levels could be affected by treatment with immunosuppressive drugs such as cyclosporin A (CsA) and mycophenolate mofetil (MMF). Treatment with CsA, but not MMF, is accompanied by nephrotoxicity, and since suPAR levels correlate with glomerular filtration rate (GFR), treatment with these drugs could indirectly modulate suPAR levels by their effect on renal function.

METHODS

We measured suPAR levels in a recent prospective multicenter crossover trial comparing the efficacy of MMF and CsA in pediatric patients with minimal change disease (MCD) and frequently relapsing steroid-sensitive nephrotic syndrome (FR-SSNS). All patients had biopsy-proven MCD and normal renal function; they were treated with each drug for 1 year in a crossover study design. Serum suPAR levels were measured before and after 1 year of therapy with MMF (n = 40) and CsA (n = 35).

RESULTS

The suPAR levels decreased after 1 year of treatment with MMF (p < 0.05). Conversely, suPAR levels increased after 1 year of treatment with CsA in the same patients (p = 0.01). These changes in suPAR levels were not correlated to the estimated glomerular filtration rate (eGFR) or changes in the GFR.

CONCLUSIONS

Data from this prospective randomized trial suggest that treatment with MMF and CsA is associated with different effects on suPAR levels in children with MCD and that these are independent of their effects on GFR.

A reassessment of soluble urokinase-type plasminogen activator receptor in glomerular disease

It has been suggested that soluble urokinase receptor (suPAR) is a causative circulating factor for and a biomarker of focal and segmental glomerulosclerosis (FSGS). Here we undertook validation of these assumptions in both mouse and human models. Injection of recombinant suPAR in wild-type mice did not induce proteinuria within 24 hours. Moreover, a disease phenotype was not seen in an inducible transgenic mouse model that maintained elevated suPAR concentrations for 6 weeks. Plasma and urine suPAR concentrations were evaluated as clinical biomarkers in 241 patients with glomerular disease from the prospective, longitudinal multi-center observational NEPTUNE cohort. The serum suPAR concentration at baseline inversely correlated with estimated glomerular filtration rate (eGFR) and the urine suPAR/creatinine ratio positively correlated with the urine protein/creatinine ratio. After adjusting for eGFR and urine protein, neither the serum nor urine suPAR level was an independent predictor of FSGS histopathology. A multivariable mixed-effects model of longitudinal data evaluated the association between the change in serum suPAR concentration from baseline with eGFR. After adjusting for baseline suPAR concentration, age, gender, proteinuria and time, the change in suPAR from baseline was associated with eGFR, but this association was not different for patients with FSGS as compared to other diagnoses. Thus, these results do not support a pathological role for suPAR in FSGS.

LPS nephropathy in mice is ameliorated by IL-2 independently of regulatory T cells activity

Immunosuppressive regulatory T cells (Tregs) have been hypothesized to exert a protective role in animal models of spontaneous (Buffalo/Mna) and/or drug induced (Adriamycin) nephrotic syndrome. In this study, we thought to define whether Tregs can modify the outcome of LPS nephropathy utilizing IL-2 as inducer of tissue and circulating Tregs. LPS (12 mg/Kg) was given as single shot in C57BL/6, p2rx7⁻/⁻ and Foxp3EGFP; free IL-2 (18.000 U) or, in alternative, IL-2 coupled with JES6-1 mAb (IL-2/anti-IL-2) were injected before LPS. Peripheral and tissue Tregs/total CD4+ cell ratio, urinary parameters and renal histology were evaluated for 15 days. IL-2 administration to wild type mice had no effect on peripheral Tregs number, whereas a significant increase was induced by the IL-2/anti-IL-2 immunocomplex after 5 days. Spleen and lymph nodes Tregs were comparably increased. In p2rx7⁻/⁻ mice, IL-2/anti-IL-2 treatment resulted in increase of peripheral Tregs but did not modify the spleen and lymph nodes quota. LPS induced comparable and transient proteinuria in both wild type and p2rx7⁻/⁻ mice. Proteinuria was inhibited by co-infusion of human IL-2, with reduction at each phase of the disease (24 -48 and 72 hours) whereas IL-2/anti-IL-2 produced weaker effects. In all mice (wild type and p2rx7⁻/⁻) and irrespective of treatment (IL-2, IL-2/anti-IL-2), LPS was associated with progressive signs of renal pathologic involvement resulting in glomerulosclerosis. In conclusion, IL-2 plays a transient protective effect on proteinuria induced by LPS independent of circulating or tissue Tregs but does not modify the outcome of renal degenerative renal lesions.

Relationship between serum soluble urokinase plasminogen activator receptor level and steroid responsiveness in FSGS

BACKGROUND AND OBJECTIVES

Soluble urokinase plasminogen activator receptor (suPAR) was initially proposed as a pathogenic and predictive biomarker of primary FSGS, but the findings were controversial. This study aimed to clarify the clinical implications of suPAR.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The study enrolled 109 patients with biopsy-proven primary FSGS who were administered prednisone between January 2011 and May 2013 and followed up for 6-24 months (median duration of follow-up, 12 months). Ninety-six healthy volunteers, 20 patients with minimal-change disease (MCD), and 22 patients with membranous nephropathy (MN) served as controls. Serum suPAR levels were measured using ELISA.

RESULTS

suPAR levels in patients with FSGS (median, 3512 [interquartile range (IQR), 2232-4231] pg/ml) were significantly higher than in healthy controls (median, 1823 [IQR, 1563-2212] pg/ml; P<0.001), patients with MCD (median, 1678 [IQR, 1476-2182] pg/ml; P<0.001), and patients with MN (median, 1668 [IQR, 1327-2127] pg/ml; P<0.001). With 3000 pg/ml used as a threshold, suPAR levels were elevated in 48.6% of patients with FSGS, in contrast to 5% of patients with MCD and 4.5% of those with MN. suPAR levels were independently associated with steroid response in patients with FSGS (odds ratio, 85.02; P=0.001). Patients who were sensitive to steroids had significantly higher suPAR levels than nonsensitive patients (median, 3426 [IQR, 2670-5655] pg/ml versus 2523 [IQR, 1977-3460] pg/ml; P=0.001). A suPAR level of 3400 pg/ml was chosen as the optimal cutoff value for steroid response. At the 6-month follow-up in 84 patients with FSGS, suPAR levels were significantly decreased in those with suPAR level ≥ 3400 pg/ml (median, 4553 [IQR, 3771-6120] pg/ml versus 3149 [IQR, 2278-3953]; P=0.002) but were unchanged in patients with suPAR level <3400 pg/ml (median, 2359 [IQR, 2023-2842] pg/ml versus 2490 [IQR, 1916-3623] pg/ml; P=0.09).

CONCLUSIONS

suPAR is specifically elevated in some patients with FSGS, which differs from the finding in patients with MCD and MN. A suPAR assay may help predict steroid response in patients with primary FSGS.

Urine soluble urokinase-type plasminogen activator receptor levels correlate with proteinuria in Puumala hantavirus infection

OBJECTIVES

Urokinase-type plasminogen activator receptor (uPAR) is upregulated during inflammation and known to bind to β3 -integrins, receptors used by pathogenic hantaviruses to enter endothelial cells. It has been proposed that soluble uPAR (suPAR) is a circulating factor that causes focal segmental glomerulosclerosis and proteinuria by activating β3 -integrin in kidney podocytes. Proteinuria is also a characteristic feature of hantavirus infections. The aim of this study was to evaluate the relation between urine suPAR levels and disease severity in acute Puumala hantavirus (PUUV) infection.

DESIGN

A single-centre, prospective cohort study.

SUBJECTS AND METHODS

Urinary suPAR levels were measured twice during the acute phase and once during convalescence in 36 patients with serologically confirmed PUUV infection. Fractional excretion of suPAR (FE suPAR) and of albumin (FE alb) was calculated.

RESULTS

The FE suPAR was significantly elevated during the acute phase of PUUV infection compared to the convalescent phase (median 3.2%, range 0.8-52.0%, vs. median 1.9%, range 1.0-5.8%, P = 0.005). Maximum FE suPAR was correlated markedly with maximum FE alb (r = 0.812, P < 0.001) and with several other variables that reflect disease severity. There was a positive correlation with the length of hospitalization (r = 0.455, P = 0.009) and maximum plasma creatinine level (r = 0.780, P < 0.001) and an inverse correlation with minimum urinary output (r = -0.411, P = 0.030). There was no correlation between FE suPAR and plasma suPAR (r = 0.180, P = 0.324).

CONCLUSION

Urinary suPAR is markedly increased during acute PUUV infection and is correlated with proteinuria. High urine suPAR level may reflect local production of suPAR in the kidney during the acute infection.

Circulating suPAR levels are affected by glomerular filtration rate and proteinuria in primary and secondary glomerulonephritis

BACKGROUND

Circulating levels of soluble urokinase-like plasminogen activator receptor (suPAR) have been associated with proteinuria and renal function in focal segmental glomerulosclerosis (FSGS). This study aimed to evaluate if circulating suPAR levels are independently associated with proteinuria in patients with non-FSGS glomerulonephritis.

METHODS

This is a cross-sectional analysis of suPAR levels on 42 patients with primary non-FSGS glomerulonephritis (group GN) and 140 patients with secondary glomerulonephritis within an autoimmune disease (group AID).

RESULTS

suPAR serum levels were significantly higher in AID patients (4,733 ± 3,073 pg/ml) than in healthy controls (1,908 ± 1,685 pg/ml; p < 0.001), whereas GN patients displayed intermediate levels (3,670 ± 2,435 pg/ml; p = 0.021). Multivariate analysis for elevated serum suPAR (>3,000 pg/ml) showed an independent association with estimated glomerular filtration rate (eGFR) <60 ml/min/1.73 m(2) [odds ratio (OR) = 4.19, 95% confidence interval (CI): 1.67-10.54, p = 0.002], proteinuria >0.5 g/day (OR = 2.97; 95% CI: 1.32-6.70; p = 0.009) and presence of secondary vs. primary GN (OR = 2.87, 95% CI: 1.25-6.23; p = 0.013). A general linear model confirmed that suPAR levels were significantly affected by proteinuria >0.50 g/day (coefficient +1,477 pg/ml), eGFR (-38 pg/ml per 1 ml/min/1.73 m(2) increase) and presence of secondary vs. primary GN (+1,368 pg/ml).

CONCLUSIONS

This study shows that elevated serum suPAR levels are associated with reduced eGFR and presence of proteinuria in both primary and secondary GN, suggesting that circulating suPAR may represent a common biomarker of renal involvement in a wide spectrum of GN.

Decreased glomerular filtration as the primary factor of elevated circulating suPAR levels in focal segmental glomerulosclerosis

BACKGROUND

Circulating factor(s) has been thought to be the underlying cause of focal segmental glomerulosclerosis (FSGS), and recent studies foster this idea by demonstrating increased soluble urokinase receptor (suPAR) levels in the serum of FSGS patients.

METHODS

To explore the possible contribution of suPAR in FSGS pathogenesis, we analyzed serum suPAR levels in 17 patients with FSGS and compared them with those in patients with steroid-sensitive nephrotic syndrome, chronic glomerulonephritis, or non-glomerular kidney diseases.

RESULTS

Serum suPAR levels in patients with FSGS were higher than those in patients with steroid-sensitive nephrotic syndrome or chronic glomerulonephritis, but not higher than those in patients with non-glomerular kidney diseases. suPAR levels negatively correlate with estimated glomerular filtration rate and were decreased after renal transplantation in patients with FSGS as well as in those with non-glomerular kidney diseases. Furthermore, 6 FSGS patients with post-transplant recurrence demonstrated that suPAR levels were not high during the recurrence.

CONCLUSIONS

Based on our results, elevated suPAR levels in FSGS patients were attributed mainly to decreased glomerular filtration. These data warrant further analysis for involvement of possible circulating factor(s) in FSGS pathogenesis.

Permeability factors in focal and segmental glomerulosclerosis

Focal and segmental glomerulosclerosis (FSGS) represents a group of glomerular disorders, identified on kidney biopsy, that progress in the histopathologic pattern of sclerosis in parts of some glomeruli. Damage to podocytes usually marks the beginning of the disease, most evident in primary FSGS. In addition to genetic predisposition, there are many acquired causes that disturb normal podocyte homeostasis and allow for the development of FSGS. The aim of this review was to summarize recent findings of the most relevant circulating permeability factors that may serve as biomarkers of active primary idiopathic FSGS and aid in the diagnosis and prediction of recurrent FSGS after kidney transplantation.

Is rituximab effective in childhood nephrotic syndrome? Yes and no

The idiopathic nephrotic syndrome (i.e. MCNS and FSGS) in children has been regarded as a disorder of T-cell function. Recent studies, however, also describe abnormalities of B-cell function. This supports the use of B-cell modulating treatment for idiopathic nephrotic syndrome (INS), especially rituximab, which has been used in other glomerular disorders as well. Many studies indicate that rituximab is effective in steroid-sensitive and -dependent nephrotic syndrome, by either inducing long-term remission or reducing relapses. In most series, children with primary (and recurrent) focal segmental glomerulosclerosis (FSGS) do not respond as well. The exact mechanisms of action of rituximab (as well as those of the other treatment options) in INS are as yet unclear. In addition to hosting mechanisms a direct stabilizing effect on the podocyte may also be of relevance, especially in FSGS. Although results are encouraging especially in steroid-sensitive patients, further studies on the clinical use of rituximab and the short- and long-term immunological effects and side-effects are necessary.

CD80 and suPAR in patients with minimal change disease and focal segmental glomerulosclerosis: diagnostic and pathogenic significance

BACKGROUND

Minimal change disease (MCD) is characterized by increased urinary excretion of CD80, whereas focal segmental glomerulosclerosis (FSGS) is associated with increased serum soluble urokinase-type plasminogen activator receptor (suPAR). The aim of the study was to assess whether the simultaneous measurement of urinary CD80 and serum suPAR helps differentiate MCD and FSGS.

METHODS

Urine and sera were collected from patients with MCD in relapse or in remission, from FSGS patients with nephrotic syndrome, and from healthy individuals. CD80 and suPAR were measured by ELISA.

RESULTS

Urinary CD80 was significantly increased in MCD patients in relapse compared with those in remission and with FSGS patients and control individuals. Serum suPAR levels were significantly higher in patients with FSGS when compared with MCD patients in relapse. Urinary suPAR showed a positive correlation with proteinuria in MCD in relapse and FSGS patients, whereas urinary CD80 correlated with proteinuria only in MCD patients in relapse.

CONCLUSION

Urinary CD80 is elevated in MCD patients in relapse compared with FSGS patients. In contrast, serum suPAR is significantly elevated in FSGS patients. The consistent pattern of these two biomarkers in MCD and FSGS suggests that these two conditions represent different entities rather than a continuum spectrum of one disease.

Rituximab in idiopathic nephrotic syndrome: does it make sense?

Idiopathic nephrotic syndrome (INS) includes three different entities: minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), and mesangial proliferative glomerulonephritis. Historically, this condition has been attributed to a T-cell disorder resulting in the secretion of a circulating factor that increases glomerular permeability to plasma proteins. The therapeutic approach to control the proteinuria of INS remains the use of drugs that have been considered to suppress the production of the "circulating factor" secreted by T cells. Recently, rituximab (RTX), a chimeric monoclonal antibody directed against the CD20 cell surface receptor expressed on B cells, has emerged as potential therapeutic agent. The number of publications reporting clinical experience with RTX in the treatment of nephrotic syndrome has greatly increased in the last few years. However, there is currently no good evidence from clinical or experimental studies that support a role of RTX in the treatment of MCD and FSGS proteinuria. In summary, there is the need for a better understanding of the pathogenesis of the proteinuria in INS and the potential role of RTX in this condition.

Heterogeneous genetic alterations in sporadic nephrotic syndrome associate with resistance to immunosuppression

In children, sporadic nephrotic syndrome can be related to a genetic cause, but to what extent genetic alterations associate with resistance to immunosuppression is unknown. In this study, we designed a custom array for next-generation sequencing analysis of 19 target genes, reported as possible causes of nephrotic syndrome, in a cohort of 31 children affected by sporadic steroid-resistant nephrotic syndrome and 38 patients who exhibited a similar but steroid-sensitive clinical phenotype. Patients who exhibited extrarenal symptoms, had a familial history of the disease or consanguinity, or had a congenital onset were excluded. We identified a genetic cause in 32.3% of the children with steroid-resistant disease but zero of 38 children with steroid-sensitive disease. Genetic alterations also associated with lack of response to immunosuppressive agents in children with steroid-resistant disease (0% of patients with alterations versus 57.9% of patients without alterations responded to immunosuppressive agents), whereas clinical features, age at onset, and pathologic findings were similar in steroid-resistant patients with and without alterations. These results suggest that heterogeneous genetic alterations in children with sporadic forms of nephrotic syndrome associate with resistance to steroids as well as immunosuppressive treatments. In these patients, a comprehensive screening using such an array may, thus, be useful for genetic counseling and may help clinical decision making in a fast and cost-efficient manner.

Sphingomyelinase-like phosphodiesterase 3b expression levels determine podocyte injury phenotypes in glomerular disease

Diabetic kidney disease (DKD) is the most common cause of ESRD in the United States. Podocyte injury is an important feature of DKD that is likely to be caused by circulating factors other than glucose. Soluble urokinase plasminogen activator receptor (suPAR) is a circulating factor found to be elevated in the serum of patients with FSGS and causes podocyte αVβ3 integrin-dependent migration in vitro. Furthermore, αVβ3 integrin activation occurs in association with decreased podocyte-specific expression of acid sphingomyelinase-like phosphodiesterase 3b (SMPDL3b) in kidney biopsy specimens from patients with FSGS. However, whether suPAR-dependent αVβ3 integrin activation occurs in diseases other than FSGS and whether there is a direct link between circulating suPAR levels and SMPDL3b expression in podocytes remain to be established. Our data indicate that serum suPAR levels are also elevated in patients with DKD. However, unlike in FSGS, SMPDL3b expression was increased in glomeruli from patients with DKD and DKD sera-treated human podocytes, where it prevented αVβ3 integrin activation by its interaction with suPAR and led to increased RhoA activity, rendering podocytes more susceptible to apoptosis. In vivo, inhibition of acid sphingomyelinase reduced proteinuria in experimental DKD but not FSGS, indicating that SMPDL3b expression levels determined the podocyte injury phenotype. These observations suggest that SMPDL3b may be an important modulator of podocyte function by shifting suPAR-mediated podocyte injury from a migratory phenotype to an apoptotic phenotype and that it represents a novel therapeutic glomerular disease target.

Urinary soluble urokinase receptor levels are elevated and pathogenic in patients with primary focal segmental glomerulosclerosis

BACKGROUND

Focal segmental glomerulosclerosis (FSGS) is a major cause of end-stage renal disease. Recent studies have proposed that plasma soluble urokinase receptor (suPAR) might be a causative circulating factor but this proposal has caused controversy. This study aimed to measure urinary suPAR levels in patients with primary FSGS and its significance in the pathogenesis of FSGS.

METHODS

Sixty-two patients with primary FSGS, diagnosed between January 2006 and January 2012, with complete clinical and pathologic data were enrolled, together with disease and normal controls. Urinary suPAR levels were measured using commercial ELISA kits and were corrected by urinary creatinine (Cr). The associations between urinary suPAR levels and clinical data at presentation and during follow up were analyzed. Conditionally immortalized human podocytes were used to study the effect of urinary suPAR on activating β3 integrin detected by AP5 staining.

RESULTS

The urinary suPAR level of patients with primary FSGS (500.56, IQR 262.78 to 1,059.44 pg/μmol Cr) was significantly higher than that of patients with minimal change disease (307.86, IQR 216.54 to 480.18 pg/μmol Cr, P = 0.033), membranous nephropathy (250.23, IQR 170.37 to 357.59 pg/μmol Cr, P <0.001), secondary FSGS (220.45, IQR 149.38 to 335.54 pg/μmol Cr, P <0.001) and normal subjects (183.59, IQR 103.92 to 228.78 pg/μmol Cr, P <0.001). The urinary suPAR level of patients with cellular variant was significantly higher than that of patients with tip variant. The urinary suPAR level in the patients with primary FSGS was positively correlated with 24-hour urine protein (r = 0.287, P = 0.024). During follow up, the urinary suPAR level of patients with complete remission decreased significantly (661.19, IQR 224.32 to 1,115.29 pg/μmol Cr versus 217.68, IQR 121.77 to 415.55 pg/μmol Cr, P = 0.017). The AP5 signal was strongly induced along the cell membrane when human differentiated podocytes were incubated with the urine of patients with FSGS at presentation, and the signal could be reduced by a blocking antibody specific to uPAR.

CONCLUSIONS

Urinary suPAR was specifically elevated in patients with primary FSGS and was associated with disease severity. The elevated urinary suPAR could activate β3 integrin on human podocytes.

suPAR and Team Nephrology

Primary focal segmental glomerulosclerosis (FSGS) accounts for nearly 10 % of patients who require renal replacement therapy. Elevated circulating levels of soluble urokinase receptor (suPAR) have been identified as a biomarker to discriminate primary FSGS from other glomerulopathies. Subsequent reports have questioned the diagnostic utility of this test. In a study in BMC Medicine, Huang et al. demonstrate that urinary soluble urokinase receptor (suPAR) excretion assists in distinguishing primary FSGS from other glomerular diseases, and that high plasma suPAR concentrations are not directly linked to a decline in glomerular filtration rate (GFR). This observation suggests that further investigation of suPAR is warranted in patients with FSGS. It should be interpreted in light of a recent report that B7-1 is expressed in the podocytes of a subset of patients with FSGS, and that blocking this molecule may represent the first successful targeted intervention for this disease. These advances highlight the rapid pace of scientific progress in the field of nephrology. Nephrologists should work together, share resources, and expedite the design of protocols to evaluate these novel biomarkers in a comprehensive and scientifically valid manner.

Administration of recombinant soluble urokinase receptor per se is not sufficient to induce podocyte alterations and proteinuria in mice

Circulating levels of soluble forms of urokinase-type plasminogen activator receptor (suPAR) are generally elevated in sera from children and adults with FSGS compared with levels in healthy persons or those with other types of kidney disease. In mice lacking the gene encoding uPAR, forced increases in suPAR concentration result in FSGS-like glomerular lesions and proteinuria. However, whether overexpression of suPAR, per se, contributes to the pathogenesis of FSGS in humans remains controversial. We conducted an independent set of animal experiments in which two different and well characterized forms of recombinant suPAR produced by eukaryotic cells were administered over the short or long term to wild-type (WT) mice. In accordance with the previous study, the delivered suPARs are deposited in the glomeruli. However, such deposition of either form of suPAR in the kidney did not result in increased glomerular proteinuria or altered podocyte architecture. Our findings suggest that glomerular deposits of suPAR caused by elevated plasma levels are not sufficient to engender albuminuria.

The p.R229Q variant of the NPHS2 (podocin) gene in focal segmental glomerulosclerosis and steroid-resistant nephrotic syndrome: a meta-analysis

While many previous studies have reported an association between the p.R229Q variant of the NPHS2 gene and focal segmental glomerulosclerosis (FSGS) or steroid-resistant nephrotic syndrome (SRNS), a conclusive relationship has not been defined. In this study, we performed a meta-analysis of the published data to investigate the impact of the p.R229Q polymorphism on FSGS and SRNS patients. Despite significant heterogeneity within some of the comparisons, the results revealed significantly higher risks of SRNS in individuals homozygous for the variant allele (OR 7.411, 95% confidence interval 1.876-29.436, p = 0.004) compared to homozygous non-variant individuals. However, the carrier rate of the p.R229Q variant was not significantly different between SRNS patients and steroid-sensitive nephrotic syndrome patients. No statistically significant differences in the p.R229Q carrier rate were observed between FSGS patients and controls or FSGS patients and patients with different pathology classifications. No notable differences in the p.R229Q carrier rate were found between patients and controls in any group with early-onset disease (onset age < 18). In conclusion, our meta-analysis suggests that for adult-onset disease (onset age > 18), the homozygous variant could be a potential predictor of hereditary nephrotic syndrome and that the p.R229Q allele cannot currently be considered a risk factor for predicting FSGS.

The novel diagnostic biomarkers for focal segmental glomerulosclerosis

Background. Focal segmental glomerulosclerosis (FSGS) is a glomerular injury with various pathogenic mechanisms. Urine proteome panel might help in noninvasive diagnosis and better understanding of pathogenesis of FSGS. Method. We have analyzed the urine sample of 11 biopsy-proven FSGS subjects, 8 healthy controls, and 6 patients with biopsy-proven IgA nephropathy (disease controls) by means of liquid chromatography tandem mass spectrometry (nLC-MS/MS). Multivariate analysis of quantified proteins was performed by principal component analysis (PCA) and partial least squares (PLS). Results. Of the total number of 389 proteins, after multivariate analysis and additional filter criterion and comparing FSGS versus IgA nephropathy and healthy subjects, 77 proteins were considered as putative biomarkers of FSGS. CD59, CD44, IBP7, Robo4, and DPEP1 were the most significant differentially expressed proteins. These proteins are involved in pathogenic pathways: complement pathway, sclerosis, cell proliferation, actin cytoskeleton remodeling, and activity of TRPC6.There was complete absence of DPEP1 in urine proteome of FSGS subjects compared with healthy and disease controls. DPEP1 acts via leukotrienes on TRPC6 and results in increased podocyte motility and proteinuria. Conclusion. The results suggest a panel of candidate biomarkers for noninvasive diagnosis of FSGS, while complete absence of DPEP1 might represent a novel marker of FSGS.

Focal segmental glomerulosclerosis: towards a better understanding for the practicing nephrologist

Focal and segmental glomerulosclerosis (FSGS) is a common histopathological lesion that can represent a primary podocytopathy, or occur as an adaptive phenomenon consequent to nephron mass reduction, a scar from a healing vasculitic lesion, direct drug toxicity or viral infection among other secondary causes. Thus, the presence of an FSGS lesion in a renal biopsy does not confer a disease diagnosis, but rather represents the beginning of an exploratory process, hopefully leading ultimately to identification of a specific etiology and its appropriate treatment. We define primary FSGS as a 'primary' podocytopathy characterized clinically by the presence of nephrotic syndrome in a patient with an FSGS lesion on light microscopy and widespread foot process effacement on electron microscopy (EM). Secondary FSGS is commonly characterized by the absence of nephrotic syndrome and the presence of segmental foot process effacement on EM. Failure to accurately differentiate between the primary and secondary forms of FSGS has resulted in many patients undergoing unnecessary immunosuppressive treatment. Here, we review some key points that may assist the practicing nephrologist to distinguish between primary and secondary FSGS.

Novel biomarkers in glomerular disease

Glomerular diseases are major contributors to the global burden of end-stage kidney disease. The clinical course and outcome of these disorders are extremely variable and difficult to predict. The clinical trajectories range from a benign and spontaneously remitting condition to a symptomatic and rapidly progressive disease. The diagnosis is based entirely on the evaluation of kidney biopsy, but this invasive procedure carries multiple risks and often fails to predict the clinical course or responsiveness to treatment. However, more recent advances in genetics and molecular biology have facilitated elucidation of novel pathogenic mechanisms of these disorders. These discoveries fuel the development of novel biomarkers and offer prospects of noninvasive diagnosis and improved prognostication. Our review focuses on the most promising novel biomarkers that have recently emerged for the major types of glomerular diseases, including immunoglobulin A nephropathy, membranous nephropathy, focal segmental glomerulosclerosis, and membranoproliferative glomerulonephritis.

Renal biopsy: use of biomarkers as a tool for the diagnosis of focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a glomerulopathy associated with nephrotic syndrome and podocyte injury. FSGS occurs both in children and adults and it is considered the main idiopathic nephrotic syndrome nowadays. It is extremely difficult to establish a morphological diagnosis, since some biopsies lack a considerable quantifiable number of sclerotic glomeruli, given their focal aspect and the fact that FSGS occurs in less than half of the glomeruli. Therefore, many biological molecules have been evaluated as potential markers that would enhance the diagnosis of FSGS. Some of these molecules and receptors are associated with the pathogenesis of FSGS and have potential use in diagnosis.

A multicenter cross-sectional study of circulating soluble urokinase receptor in Japanese patients with glomerular disease

Elevated serum-soluble urokinase receptor (suPAR) levels have been described in patients with focal segmental glomerulosclerosis (FSGS) in several different cohorts. However, it remains unclear whether this is the case for Japanese patients and whether circulating suPAR can be clinically useful as a diagnostic marker. To determine this, we measured serum suPAR levels in 69 Japanese patients with biopsy-proven glomerular diseases in a cross-sectional manner. The serum suPAR levels showed a significant inverse correlation with renal function by univariate (R(2) of 0.242) and multivariate (β=0.226) analyses. Even after excluding patients with renal dysfunction, no significant difference in the suPAR levels was detected among the groups. Receiver operating characteristic analysis and measures of the diagnostic test performance showed that suPAR was not a useful parameter for differentiating FSGS from the other glomerular diseases (AUC-ROC: 0.621), although a small subgroup analysis showed that patients with FSGS, treated with steroids and/or immunosuppressants, had significantly lower suPAR levels. Patients with ANCA-associated glomerulonephritis had significantly higher levels of suPAR compared with the other disease groups, which may be owing to their lower renal function and systemic inflammation. Thus, suPAR levels are significantly affected by renal function and have little diagnostic value even in patients with normal renal function.

Immunopathogenesis of idiopathic nephrotic syndrome with relapse

Idiopathic change nephrotic syndrome (INS), the most frequent glomerular disease in children and young adults, is characterized by heavy proteinuria and a relapsing remitting course. Although the mechanisms underlying the pathophysiology of proteinuria remain unclear, clinical and experimental observations suggest that lymphocyte and podocyte disturbances are two sides of the disease. The current hypothesis suggests that immune cells release a putative factor, which alters podocyte function resulting in nephrotic proteinuria. Besides T-cell abnormalities, recent evidence of B-cell depletion efficacy in sustained remissions added a new challenge in understanding the immunological mechanisms of INS. In this review, we discuss recent insights related to podocyte disorders occurring in INS and their relevance in human diseases.

Podocyte pathology and nephropathy - sphingolipids in glomerular diseases

Sphingolipids are components of the lipid rafts in plasma membranes, which are important for proper function of podocytes, a key element of the glomerular filtration barrier. Research revealed an essential role of sphingolipids and sphingolipid metabolites in glomerular disorders of genetic and non-genetic origin. The discovery that glucocerebrosides accumulate in Gaucher disease in glomerular cells and are associated with clinical proteinuria initiated intensive research into the function of other sphingolipids in glomerular disorders. The accumulation of sphingolipids in other genetic diseases including Tay-Sachs, Sandhoff, Fabry, hereditary inclusion body myopathy 2, Niemann-Pick, and nephrotic syndrome of the Finnish type and its implications with respect to glomerular pathology will be discussed. Similarly, sphingolipid accumulation occurs in glomerular diseases of non-genetic origin including diabetic kidney disease (DKD), HIV-associated nephropathy, focal segmental glomerulosclerosis (FSGS), and lupus nephritis. Sphingomyelin metabolites, such as ceramide, sphingosine, and sphingosine-1-phosphate have also gained tremendous interest. We recently described that sphingomyelin phosphodiesterase acid-like 3b (SMPDL3b) is expressed in podocytes where it modulates acid sphingomyelinase activity and acts as a master modulator of danger signaling. Decreased SMPDL3b expression in post-reperfusion kidney biopsies from transplant recipients with idiopathic FSGS correlates with the recurrence of proteinuria in patients and in experimental models of xenotransplantation. Increased SMPDL3b expression is associated with DKD. The consequences of differential SMPDL3b expression in podocytes in these diseases with respect to their pathogenesis will be discussed. Finally, the role of sphingolipids in the formation of lipid rafts in podocytes and their contribution to the maintenance of a functional slit diaphragm in the glomerulus will be discussed.

An emerging molecular understanding and novel targeted treatment approaches in pediatric kidney diseases

The evaluation and treatment of the heterogeneous group of kidney diseases poses a challenging field in pediatrics. Many of the pediatric disorders resulting in severe renal affection are exceedingly rare and therapeutic approaches have remained symptomatic for most of these disease entities. The insights obtained from cellular and molecular studies of rare disorders by recent genetic studies have now substantially changed our mechanistic understanding of various important pediatric renal diseases and positive examples of targeted treatment approaches are emerging. Three fields of recent breathtaking developments in pediatric nephrology are the pathophysiology of nephrotic syndrome and proteinuria, the molecular mechanisms underlying atypical hemolytic uremic syndrome, and the genetics and cellular biology of inherited cystic kidney diseases. In all three areas, the combined power of molecular basic science together with deeply characterizing clinical approaches has led to the establishment of novel pathophysiological principles and to the first clinical trials of targeted treatment approaches.

Therapeutic plasma exchange for the treatment of pediatric renal diseases in 2013

Therapeutic plasma exchange is an extracorporeal treatment modality that removes systemic circulating pathologic factors or replaces absent plasma components and plays a role in many nephrologic conditions. It presents a number of technical challenges in the pediatric population but has become an increasingly common practice in pediatric nephrology over the past several decades. While prospective evidence is often lacking, our increased understanding of the molecular pathogenesis underlying many pediatric renal diseases provides sound reasoning for the use of plasma exchange in treating these conditions. This review will present the currently accepted indications for plasma exchange in children, the technical aspects of the procedure and its potential complications.

Podocyte effacement closely links to suPAR levels at time of posttransplantation focal segmental glomerulosclerosis occurrence and improves with therapy

BACKGROUND

Focal segmental glomerulosclerosis (FSGS) recurs after kidney transplantation in more than 30% of cases and can lead to allograft loss. Serum soluble urokinase-type plasminogen activator receptor (suPAR) is implicated in the pathogenesis of native and recurrent FSGS.

METHODS

We conducted a retrospective study of 25 adults with posttransplantation FSGS. We investigated the relationship between suPAR levels and podocyte changes and the impact of therapy on podocyte structure. We assessed response to therapy by improvement in proteinuria, allograft function, and resolution of histologic changes.

RESULTS

A median (interquartile range) of 15 (10-23) plasmapheresis sessions was administered; 13 of the subjects also received rituximab. Median pretreatment suPAR levels were higher among those with severe (≥75%) versus those with mild (≤25%) podocyte foot process effacement (13,030 vs. 4806 pg/mL; P=0.02). Overall, mean±SD of proteinuria improved from 5.1±3.8 to 2.1±2.8 mg/dL (P=0.003), mean podocyte effacement decreased from 57%±33% to 22%±22% (P=0.0001), estimated glomerular filtration rates increased from median (interquartile range) of 32.9 (20.6-44.2) to 39.3 (28.8-63.4; P<0.0001), and suPAR levels decreased from a median of 6.781 to 4.129 pg/mL (P=0.02) with therapy.

CONCLUSIONS

Podocyte effacement is the first pathologic manifestation of FSGS after transplantation. The degree of podocyte effacement correlates with suPAR levels at time of diagnosis. Response to therapy results in significant reduction of suPAR levels and complete or significant improvement of podocyte effacement.

Diagnostic tests and treatment options in glomerular disease: 2014 update

Glomerular diseases historically have been challenging disorders to comprehend and treat for patients and physicians alike. Kidney biopsy is the gold standard of diagnosis, but the link between pathophysiology and the histologic representation of kidney injury has remained elusive in many of these diseases. As a result, treatment of glomerular disease usually involves therapies that are not specific to disease pathogenesis, such as blockade of the renin-angiotensin-aldosterone system and various immunosuppression regimens. Recent research has resulted in greater insight into some glomerular diseases, leading to the hope that new diagnostic tests and treatments targeting disease-specific mechanisms are on the horizon. We review recent progress on the understanding, diagnosis, and treatment of 4 glomerular diseases: immunoglobulin A nephropathy, focal segmental glomerulosclerosis, the C3 glomerulopathies, and idiopathic membranous nephropathy.

Urine but not serum soluble urokinase receptor (suPAR) may identify cases of recurrent FSGS in kidney transplant candidates

BACKGROUND

Recently, serum soluble urokinase receptor (suPAR) has been proposed as a cause of two thirds of cases of focal segmental glomerulosclerosis (FSGS). It was noted to be uniquely elevated in cases of primary FSGS, with higher levels noted in cases that recurred after transplantation. It is also suggested as a possible target and marker of therapy.

METHODS

We studied serum and urine suPAR from pretransplantation banked samples from 86 well-characterized kidney transplant recipients and 10 healthy controls to determine its prognostic utility. Causes of native kidney disease were primary FSGS, diabetic nephropathy, membranous nephropathy, immunoglobulin A nephropathy, and autosomal dominant polycystic kidney disease. suPAR was measured using a commercially available enzyme-linked immunosorbent assay kit. Urinary suPAR was indexed to creatinine.

RESULTS

Both serum and urine suPAR correlated with proteinuria and albuminuria. Serum suPAR was found to be elevated in all transplant candidates with advanced renal disease compared with healthy controls and could not differentiate disease diagnosis. Urine suPAR was elevated in cases of recurrent FSGS compared with all other causes of end-stage renal disease. Recurrent FSGS cases had substantially higher proteinuria compared with all other cases. However, elevated urinary suPAR showed a trend in providing additional prognostic information beyond proteinuria in the small cohort of recurrent FSGS cases.

CONCLUSION

In advanced renal disease, elevated serum suPAR is not unique to FSGS cases. Urinary suPAR appears to be higher in cases of FSGS destined for recurrence and merits further evaluation.

Primary focal and segmental glomerulosclerosis and soluble factor urokinase-type plasminogen activator receptor

Primary focal and segmental glomerulosclerosis (FSGS) may be due to genetic or acquired etiologies and is a common cause of nephrotic syndrome with high morbidity that often leads to end-stage renal failure. The different available therapeutic approaches are unsuccessful, in part due to partially deciphered heterogeneous and complex pathophysiological mechanisms. Moreover, the term FSGS, even in its primary form, comprises a histological description shared by a number of different causes with completely different molecular pathways of disease. This review focuses on the latest developments regarding the pathophysiology of primary acquired FSGS caused by soluble factor urokinase type plasminogen activator receptor, a circulating permeability factor involved in proteinuria and edema formation, and describes recent advances with potential success in therapy.

Glomerular diseases: FSGS

FSGS is a lesion, not a disease. The separation into primary FSGS (a result of immunologic-mediated injury) versus secondary FSGS (related to a variety of causes) is often difficult. Even when this particular issue is carefully evaluated, the therapeutic implications are not always apparent. Newer literature on both biomarker discovery and on the genetic basis of FSGS is reviewed in this context. In addition, the thorny implications of obesity as it relates to the FSGS lesion are discussed. An overall practical algorithmic approach to the management and treatment of the FSGS lesion that integrates these controversial overlap areas is suggested.

Management of severe recurrent focal segmental glomerulosclerosis through circulating soluble urokinase receptor modification

Circulating soluble urokinase receptor (suPAR) was recently identified as one of the causes responsible for native and recurrent focal segmental glomerulosclerosis (FSGS) through overactivation of podocyte β(3) integrin. Here, we discuss the management of a patient with very high suPAR serum levels and FSGS recurrence. The suPAR reduction using plasmapheresis and immunoadsorption allowed for lowering of suPAR and reduced podocyte β(3) integrin activation and proteinuria. The patient is successfully weaned to bimonthly suPAR removal treatments with improved renal parameters. In summary, we provide an approach for the successful management of severe recurrent FSGS using available therapies with biomarker guidance.